1. Field of the Invention
The present invention relates to a material for the formation of a polybenzazole (imidazole, oxazole or thiazole) film having high heat resistance and a low dielectric constant, as well as a polymer and a dielectric film using the material. More specifically, it relates to a material for the formation of a dielectric film which is useful as a semiconductor part, as well as a polymer and a dielectric film using the material.
2. Description of the Related Art
Polybenzazoles having an adamantane skeleton are useful as highly heat-resistant resins (Journal of Polymer Science, Part A-1 (1970), 8(12), p. 3665–3666). In particular, highly crosslinked polybenzazoles using a trifunctional or tetrafunctional adamantane derivative involve a multitude of molecular-scale voids, have a low relative dielectric constant, satisfactory mechanical strength and heat resistance and are thereby very useful as materials for interlayer dielectrics (Japanese Unexamined Patent Application Publication (JP-A) No. 2001-332543). These highly crosslinked polybenzazoles can be prepared, for example, by heating a material in the presence of a condensing agent such as a polyphosphoric acid. However, the resulting highly crosslinked resin is hardly soluble in solvent and cannot be significantly applied to a substrate by coating to form a thin film having a sufficient thickness as an interlayer dielectric.
A thin film of a wholly aromatic chain polybenzazole is formed by a method, in which an aldehyde derivative as a material monomer is spread over an aqueous solution of an amine as another material monomer to form a film by polymerization on a gas-liquid interface; the film is laminated on a substrate by a horizontal attachment method and is subjected to a thermal treatment in the air to form a thin film of a polybenzazole (Japanese Unexamined Patent Application Publication (JP-A) No. 62-183881). However, the method is not suitable for industrial production, since it takes quite a long time to form the thin film. In addition, the precursor polyimine is subjected to an oxidative thermal treatment in a final process, and the resulting polybenzazole film may be possibly oxidized, thus a lower dielectric constant as a dielectric film is not expected.
In addition, adamantanepolycarboxylic acids and aromatic polyamines used as material monomers have a significantly high polarity as a compound and are soluble in quite limited types of solvents. In particular, these monomers are hardly soluble in a solvent having a relatively low polarity, and a film having a thickness of several hundreds of nanometers required as an interlayer dielectric for a semiconductor device cannot be significantly formed. Thus, satisfactory dielectric films of highly crosslinked polybenzazoles using a trifunctional or tetrafunctional adamantane have not been formed.